Method for the manufacture of acrylic fibers



Nov. 26,

KNOT STRENGTH ld) 1963 HIROFUMI NAGATA ETAL METHOD FOR THE MANUFACTURE OF ACRYLIC FIBERS Filed Sept. 20, 1961 ELONGATION AND KNOT STRENGTH FIGJ.

ELONGATIO N TIME AND COEFFICIENT OF RELAXATION,

AND KNOT STRENGTH RELAXATION COEFF.

FIG.2.

I KNOT STRENGTH KNOT STRENGTH (91d) TIME OF RELAXATION (sec) NECESSITY FOR CONTINUITY OF STgETCHING AND RELAXATION COEFFICIENT OF RELAXATION ("/o) FIG.3.

KNOT STRENGTH /d) o l I RETAINING TIME BETWEEN STRETGHING AND RELAXATION (sec) United States Patent ()1 3,112,161 METHOD FOR THE MANUFACTURE 9F ACRYLIC FBERS Hirofumi Nagata, Masahlko Talrikawa, Shohei Kuriolta,

and Kiyoslii Sakai, ltano-gun, Japan, assignors to Toho Rayon Kabushiki Kaisha, Tokyo, .lapan, a corporation of Japan Filed Sept. 26, 1% Ser. No. 13?,413 Claims priority, application Japan Sept. 24, 196i) 1 Claim. (Cl. 18-54) The present invention relates to a method for the manufacture of excellent acrylic fibers by consecutive treatments, such as water-rinsing under tension, stretching and reh .ng in hot water bath and so forth for filaments spun at room temperature into a low concentration coagulating bath from a spinning solution comprising acrylonitrile polymer or copolymers in an aqueous zinc chloride solution.

An object of the present invention is to avoid unfavorable effects of salts remaining in fibers on qualities of same. The salt residue is regarded as a general defect in the spinning method which uses a spinning solution comprising aqueous zinc chloride solution of acrylonitrile. Another object is to improve the strength and resilience of fibers obtained by the spinning method.

Hitherto, in the usual method of manufacturing syn thetic fibers from a spinning solution comprising acrylonitrile polymer as a fiber forming component in a solvent of aqueous zinc chloride solution, in comparison with methods with good organic solvents employed, there have been tendencies for fiber structure to be coarse and for salts to remain in the spun fibers, which result in fragility, loss of transparency, and the lowering of mechanical strengths and resiliency of produced fibers. Several in 'est ations or propositions have been reported on the preparation of spinning solutions and the desalting treatment to avoid the disadvantages above mentioned. However, in considering the qualities of such fibers, the improvements attained so far by those investigations have not been satisfactory. Even though high tensile strength could be obtained, no sufiicient toughness (knot strength) and elasticity which are inevitably necessary for textile fibers have been obtained in such cases. Thus, further improvement has een urgently required.

According to the present invention, a novel method is proposed by which the above-mentioned requirements may be satisfied by applying particular treatments to the stretching and relaxation and so forth of spun filament with respect to a spinning solution and coagulating bath. T he process of this invention is characterized in that:

(l) A polymer solution of an average concentration of zinc chloride from 50 to 60% may be used satisfactorily as a spinning solution, which has been obtained by polymerizing acrylonitrile alone or acrylonitrile added with a comonomer in an aqueous zinc chloride solution of a relatively high concentration:

(2) in the first step, the spinning is effected in a relatively low concentration bath of coagulant having the same composition as that of the above-mentioned solvent at an ordinary temperature.

Hitherto, various investigations have been conducted in reference to the concentration and temperature of a coagulant bath for the spinning of acrylonitrile polymer in an aqueous zinc chloride solution. It is referred to, for instance in the specification to US. Patent No. 2,790,700, that a relatively high concentration bath of approximately from 25 to 45% is preferable and a temperature near the ordinary temperature below 30 C. is op From the result of the investigation conducted by the present inventors, however, it has become evident that those working conditions are not always satisfactory ice for producing good final fiber products, and that when the concentration range is lower than that in the abovementioned process, i.e. 10 to 20% range, and the spinning operation is carried out at an ordinary temperature, the spinning operation will be simpler and also the concentration may be easier to control. Furthermore, it has been ascertained that the latter conditions i.e., a lower concentration range at around the ordinary temperature, is favorable as an industrial operation or convenient also for the subsequent desalting water rinsing operation.

(3) The second ste that is, the water rinsing operation is carried out for spun fibers at an ordinary temperature or in hot water below C. under slight tension.

In this case, a stretching may be effected to approximately 1 to 4 times the original length under such a tension that does not break fibers.

(4) The third step of operation, that is, stretching and relaxation are carried out, in such a manner that water rinsed fibers are first stretched to more than 300% elongation in boiling water at above C. and thereafter are instantly relaxed in boiling water at the same temperature or thereabove.

In the stretching operation according to this operation, tows showing generally a high water-retaining state after water rinsing are stretched at least 300% in a boiling water bath, or fibers rinsed in water and dried are stretched at least 300% under no tension in a boiling water bath, after thorough adjustment of moisture in a water bath at a temperature at least near that of the stretching bath. The relaxation process should be effected on tows instantly from the stretching in such a way that they may be relaxed continuously at the same temperature or above as used in stretching without lowering the temperature of tows.

In the following, the present invention is described in further detail in connection with the accompanying drawings in which FIG. 1 is a graph of the relation between the knot strength and elongation:

FIG. 2 is a graph of the relations between the time and rate of relaxation and between the time of relaxation and the knot strength of final fibers obtained; and

Fl. 3 is a graph of the relation between the knot strength of fibers and the time interval from the stretching to the relaxation process.

Both the stretching and relaxation operations must be performed in an excess of water content, or in liquid bath, and continuity between both operations must be sustained, that is, the operations should be carried out so that the time interval between them may not be so long that a lowering of the temperature of tows or variations of water content can take place.

The lowering of knot strength due to the increase of time interval between the stretching and the subsequent relaxation operations, as shown in PEG. 3, must be avoided by either continuously conducting both operations in the same bath or by retaining the temperature of connecting rollers between a pair of baths by feeding hot water to said rollers.

Considering a substantial improvement of properties of final yam obtained, the degrees of stretching and relaxation are determined appropriately, and from a practical point of view, as illustrated in FIG. 1, the stretching is required to be at least 300%. On the other hand, the qualities of fibers obtained are not substantially affected by an interval of time for stretching, unless it is within the range of ordinary industrial spinning velocity.

Relation of the time of relaxation with rate of relaxation on one hand and with the knot strength of final fibers, on the other hand is shown in FIG. 2. Thus, it is preferable to perform free shrinkage under no tension, at least from 10 to 40% rate of relaxation for above 30 seconds of relaxation treatment, preferabl" in a boiling water bath. When the relaxation is continued for a period of time longer than 30 seconds, a relaxation will approach equilibrium, and variation in the rate of relaxation is hardly observed, therefore knot strength of fiber obtained is 5 nearly a constant value.

The fibers obtained by the method according to this invention show strikingly improved qualities as illustrated in Table 1.

TABLE 1 Dry strength/not strength 80-l05%. Dry elongation/ knot elongation 92-98 Hot water shrinking rate 1% max. Youngs modulus 55-70 g./d. Elasticity recovering rate 2% elongation, 98-99%. Elasticity recovering rate 5% elongation, 80-85%. Whiteness W=0.9.

Furthermore, the salt remaining in fibers is as shown in Table 2, and can be lowered down to a range practically negligible in the last step of operation.

92 parts acrylonitrile, 8 parts methyl methacrylate and 0.1 part ammonium persulfate were polymerized in 900 parts of 57% aqueous zinc chloride solution at 50 C. The resulting solution was used as a spinning solution, which was spun out into a spinning bath of 20% aqueous zinc chloride solution at 20 C. The spun fiber was directly rinsed in water at room temperature for several minutes. The salt remaining in the water rinsed fibers was 0.65% and the water content was 200%.

In the next place, the water rinsed fibers were stretched to over 300% elongation in a boiling water bath, and soon after they were thoroughly relaxed under no tension.

The relaxed fibers were dried over a heating drum and results in fibers having the properties as shown in the following table:

Denier 3.00 Dry strength (g./d.) 3.17 Knot strength (g./d.) 2.89 Dry elongation (percent) 40.3 Knot elongation (percent) 38.0

Example 2 The spinning solution of the same composition as that of solution used in Example 1 was spun into the same spinning bath. The spun fibers were instantly rinsed in a multiple type water rinsing bath, the temperatures of same being consecutively raised. However, in order to avoid a loss of transparency due to abrupt heating, heating at above C. was avoided. Moreover, during such water rinsing, the fibers were put under a slight tension incapable of breaking the fibers. In the particular example, the spinning velocity was twice the ordinary industrial spinning velocity. Thereafter the rinsed fibers were dried. Then, the dried fibers were put into a boiling water bath at 95 C. and heated thoroughly, and then the water content was adjusted to a water retaining ratio of 200%. The fibers were stretched to a 400% elongation in the boiling water bath, and immediately relaxed under no tension in the boiling water bath. The relaxed fibers were dried at 120 C. over a drying drum without tension and fibers of the properties as shown in the following table were obtained:

Denier 2.99 Dry strength (g./d.) 2.49 Knot strength (g./d.) 2.24 Dry elongation (percent) 25.5 Knot elongation (percent) 20.2 Hot water relaxation ratio 0.7 Youngs modulus (g./d.) 60

What we claim is:

A method for the manufacture of acrylic fibers comprising spinning into filaments a polymer solution containing at least acrylonitrile and a solvent containing 50-60% zinc chloride into a coagulating bath containing 10-20% zinc chloride at a temperature below 30 C., rinsing said filaments in an aqueous medium at room temperature, stretching the rinsed filaments more than 300% in water at a temperature above C., and then relaxing the stretched filaments in water at a temperature above 95 C. for a period of more than thirty seconds.

References Cited in the file of this patent FOREIGN PATENTS 816,841 Great Britain July 22, 1959 

